Abstract

Background:
One of the most important factors in inducing the logarithmic growth of Streptococcus mutans, is a diet containing fermentable carbohydrates such as sucrose. Objectives: The aim of the current research was to compare the ability of ordinary and probiotic chocolate to induce or inhibit the growth of S. mutans.

Materials and Methods:
Lactobacillus rhamnosus, L. plantarum and L. acidophilus as probiotic strains, were cultivated on MRS agar for 24 hours at 35 C in 5% CO2. S. mutans which is a dominant factor in causing dental plaque, was isolated from 20 samples of dental plaque and caries lesions in adults on Streptococcus selective agar medium, and diagnosed by routine biochemical tests. The antimicrobial effect of three probiotic strains on S. mutans was evaluated by the deferred cross-streak method and susceptibility through the disk diffusion test. The antimicrobial effect of the probiotic supernatant powder was determined by a dilution method. Probiotic strains were added to dark chocolate with a concentration of 108 CFU/mL and their antimicrobial effect on S. mutans was evaluated by the disk diffusion susceptibility method. Survival of the probiotic strains in chocolate and pH shifts were studied in different environmental storage conditions.

Results:
The results showed that S. mutans was the dominant strain in all of the 20 dental plaque samples. L. plantarum showed the most antimicrobial effect on S. mutans with the maximum diameter of growth inhibitory zone, 35 mm and 78 78 mm in the disk diffusion method and deferred cross-streak method, respectively. Probiotic supernatant powder inhibited S. mutans strains in concentrations of 500-700 and 100-300 mg/ml at t = 0 and t = 24, respectively. Comparing the results in terms of maintenance and storage of probiotic chocolate, it showed that the best condition to keep this chocolate is at 4? C (refrigerated) with a probiotic survival of 25 to 30 days. The pH level during this period decreased from a pH of 5 to 4. Probiotic chocolate containing L. rhamnosus was shown to have the greatest antimicrobial effect on S. mutans with a maximum diameter of growth inhibitory zone of 75 mm during 59 days storage at an ambient temperature and 4 C.

Conclusions:
These results suggest that probiotic chocolate is able to inhibit the growth of S. mutans rather than ordinary chocolate.